A bipolar battery refers to a battery in which electrodes each including a current collector, a positive electrode active material layer disposed on a first face of the current collector, and a negative electrode active material layer disposed on a second face of the current collector are stacked with a separator interposed therebetween. Bipolar batteries have been widely used as power supplies for electric vehicles and various electronic devices since they relatively easily conduce, for example, an increase in voltage, a reduction in parts count, a reduction in resistance between cells, and an increase in energy density owing to space savings.
Patent Literature 1 discloses a bipolar battery including a separator holding an electrolyte layer formed of a polymer gel electrolyte or a liquid electrolyte, and a sealing resin disposed by molding on an outer periphery of the separator to prevent a liquid junction (short circuit) due to exudation of an electrolytic solution from the electrolyte portion.
Patent Literature 2 discloses a bipolar battery for which a nonaqueous electrolytic solution is employed, the bipolar battery including: a sealing member containing a modified polyolefin resin graft modified using a compound including an ethylenic double bond and an epoxy group in the same molecule; and a bipolar electrode that is free from electrolytic solution exudation and is excellent in sealing property.
In a bipolar battery, battery elements are coated with resin which may decrease the heat transferability, that is, the ability of the battery to transfer heat generated in the battery to the outside. In view of this, Patent Literature 3 proposes a secondary battery as a bipolar battery capable of efficient dissipation of heat generated in the battery to the outside, by use of ceramic with high electrical resistance and excellent heat transferability, as a material for a battery coating member.
In an alkaline secondary battery, nickel hydroxide and manganese dioxide to be used as a positive electrode active material each are a metal oxide with considerably low conductivity. In order to overcome this disadvantage, for example, Patent Literature 4 discloses an active material obtained by adding a higher-order cobalt oxide as a conductive agent to nickel hydroxide. According to this active material, the higher-order cobalt oxide forms a conductive network between the nickel hydroxide particles. This conductive network promotes a charge-discharge reaction at the entire nickel hydroxide particles, leading to an increase in capacity.